Thermally expandable microcapsule,process for producing molded foam, and molded foam

ABSTRACT

Thermo-expansive microcapsule comprising: a polymeric shell produced by polymerizing 15 to 75 weight % of a nitrile monomer, 10 to 65 weight % of a monomer having a carboxyl group, 0.1 to 20 weight % of a monomer having an amide group and 0.1 to 20 weight % of a monomer having a cyclic structure in its side chain; and a blowing agent encapsulated in the polymeric shell.

FIELD OF INVENTION

The present invention relates to thermo-expansive microcapsules andtheir application, more particularly, to thermo-expansive microcapsules,which have superior resistance against heat and solvents and exhibitsuperior expanding performance in a temperature range of 200° C. andhigher, the production process of foamed and molded product thereof, andthe foamed and molded product.

TECHNICAL BACKGROUND

Various processes for producing thermo-expansive microcapsules, whereinthermoplastic polymer is used for micro-encapsulating a volatileexpanding agent having a gasification point lower than the softeningpoint of said polymer, have been studied. An overall process forproducing thermo-expansive microcapsules is described in Japanese PatentPublication No. Sho 42-26524, and a process for producingthermo-expansive microcapsules having polymeric shell wall of uniformsickness is described in U.S. Pat. No. 3,615,972.

Although those processes can produce thermo-expansive microcapsules,they cannot produce thermo-expansive microcapsules sufficientlyexpansive in high temperature region of 200° C. and higher.

Japanese Patent Laid-Open No. Hei 9-19635 disclosed a production processof heat resistant thermo-expansive microcapsules, wherein 80% or more ofan acrylonitrile monomer are employed for producing thermo-expansivemicrocapsules. Thermo-expansive microcapsules are usually applied to aprocess wherein the microcapsules are heated near to their maximumexpanding temperature. The microcapsules produced with 80% or more of anacrylonitrile monomer have limited heat resistance, and do not exhibitsufficient expanding performance at 200° C. or higher.

WO99/46320 disclosed a production process for thermo-expansivemicrocapsules with acrylonitrile, N-substituted maleimide, a monomer ofwhich homopolymer has a Tg (glass-transition point) from 50 to 200° C.,and unsaturated carboxylic acid. In this method a preferable ratio ofthe unsaturated carboxylic acid is 5 weight percent or less and a ratiogreater than 5 weight percent decreases the expanding performance of theresultant microcapsules.

WO99/43758 disclosed a production process of highly heat resistantmicrocapsules wherein the functional groups in shell wall materialcrosslink each other when the microcapsules are expanded with heat.

Although the process can provide highly heat-resistant microcapsules,the shell wall of the expanded microcapsules has properties ofthermo-setting resin, i.e., poor elasticity and brittleness like glass,due to the crosslinking of the functional groups in the shell wallmaterial during expanding with heat. For this reason, the microcapsulescan only be applied under limited conditions and thus to limited enduses.

Recently, processes for producing foamed and molded products whereinthermo-expansive microcapsules are mixed in rubber or resin and expandedwith heat in molding the mixture have been proposed. Those processes areadvantageous for introducing discrete and uniform air bubbles in moldedproducts easily, though it was difficult in the foaming with foamingchemicals.

For example, Japanese Patent Laid-Open No. Sho 59-1541 disclosed aprocesses for producing expansive rubber composition containingthermoplastic resin hollow particles in which a blowing agent isencapsulated; Japanese Patent Laid-Open No. Sho 59-138420 disclosed aprocess for producing expanded products by blending an expanding agentsimilar to microcapsules in rubber or plastics; and Japanese PatentLaid-Open No. Hei 10-152575 disclosed a process for producing foamed andmolded products by blending thermo-expansive microcapsules inthermoplastic resin and processing the blend in extrusion orinjection-molding. However, the foamed and molded products of expansiverubber or thermoplastic resin produced in accordance with the processesdescribed in those patents shrink after the expansion of blendedmicrocapsules and thus their weight is not satisfactorily reduced.

Japanese Patent Laid-Open No.2002-226620 disclosed a production processof light-weight molded products containing thermo-expansive microspheresof which polymeric shell wall contains 80 weight percent or more of anitrile monomer. Even with the process, it is difficult to providesufficiently expanded light-weight molded products when the products areprocessed at a temperature higher than the maximum expanding temperatureof the thermo-expansive microspheres.

Recently there is an increasing demand for the development of moreheat-resistant thermo-expansive microcapsules, which are applicable invarious fields. In a process for producing highly foamed and moldedproducts by blending thermo-expansive microcapsules with resin,thermo-expansive microcapsules having a maximum expanding temperaturehigher than the heating temperature of the resin is preferable forexpanding the blend with heat to introduce discrete air bubbles in theresin.

Highly foamed molded products can be produced with the conventionalthermo-expansive microcapsules in a process wherein thermoplastic resinblended with thermo-expansive microcapsules is heated at comparativelylow temperature, 80 to 160° C. to form the blend. On the contrary,sufficiently foamed product cannot be produced with conventionalthermo-expansive microcapsules in a process wherein thermoplastic resin,rubber, or thermoplastic elastomer is knead with microcapsules andprocessed at 150° C. or higher temperature, because of insufficient heatresistance of those conventional thermo-expansive microcapsules.

The inventors of the present invention have found through theirinvestigation that thermo-expansive microcapsules having superior heatresistance can be produced by forming the shell wall of the capsuleswith polymer comprising a nitrile monomer and a monomer having acarboxyl group in its molecule.

Although the thermo-expansive microcapsules of which shell wallcomprises with a nitrile monomer and a monomer having a carboxyl groupin its molecule as major component are heat-resistant, they sometimesfail to expand enough depending on processing conditions, such askneading into resins, etc.

With further investigation, the inventors found a production process forthermo-expansive microcapsules of the present invention, wherein anitrile monomer, a monomer having a carboxyl group in its molecule, amonomer having an amide group in its molecule, and a monomer having acyclic structure in its side chain are employed to producethermo-expansive microcapsules having superior heat and solventresistance and excellent expanding performance in broad temperaturerange in high temperature region, and applicable in foaming and moldingthermoplastic resin and thermo-setting resin to be molded at 200° C. orhigher temperature.

The microcapsules mentioned above rarely change their color in resinsowing to their superior heat resistance to that of conventionalthermo-expansive microcapsules, and contribute to producing foamed andmolded products retaining high degree of whiteness even after processingat 200° C.

DISCLOSURE OF INVENTION

1. The present invention provides a thermo-expansive microcapsulecomprising: a polymeric shell produced by polymerizing 15 to 75 weight %of a nitrile monomer, 10 to 65 weight % of a monomer having a carboxylgroup, 0.1 to 20 weight % of a monomer having a amide group and 0.1 to20 weight % of a monomer having a cyclic structure in its side chain;and a blowing agent encapsulated in the polymeric shell.

2. The polymeric shell of said thermo-expansive microcapsule ischaracterized by the monomer components further containing 3 weight % orless of a monomer which has two or more of polymerizable double bonds inits molecules (cross-linking agents).

3. The polymeric shell of said thermo-expansive microcapsule ischaracterized by having a glass-transition point (Tg) of 120° C. orhigher.

4. The polymeric shell of said thermo-expansive microcapsule ischaracterized by containing 1 to 25 weight percent of inorganicsubstances.

5. Said thermo-expansive microcapsule is characterized by having amaximum expanding temperature of 200° C. or higher.

6. The production process of foamed and molded products wherein discreteair bubbles are introduced in the products by blending thethermo-expansive microcapsule described in claims 1 to 5 with rubber orresin and by heating the blend to expand the microcapsule.

7. The foamed and molded products containing the thermo-expansivemicrocapsule described in claims 1 to 5.

The thermo-expansive microcapsules of the present invention arecharacterized by polymeric shell wall which is formed with polymercomprising 15 to 75 weight percent of a nitrile monomer, 10 to 65 weightpercent of a monomer having a carboxyl group, 0.1 to 20 weight percentof a monomer having an amide group, and 0.1 to 20 weight percent of amonomer having a cyclic structure in its side chain; and a blowing agentencapsulated in the shell wall. The polymeric shell wall preferablycontains 1 to 25 weight percent of inorganic substances. The foamed andmolded products of the present invention are characterized by containingsaid thermo-expansive microcapsules.

The nitrile monomers applicable to the present invention are, forexample, acrylonitrile, methacrylonitrile, α-chloracrylonitrile,α-ethoxyacrylonitrile, fumaronitrile and the mixture of any combinationof them, and the like. Among those, acrylonitrile and/ormethacrylonitrile are preferable. The amount of the nitrile monomer mayrange from 15 to 75 weight percent, preferably from 25 to 65 weightpercent, of the polymeric shell wall. Polymeric shell wall containingless than 15 weight percent of the nitrile monomer has poor performanceas vapor barriers and cannot expand sufficiently.

The monomers having a carboxyl group are, for example, acrylic acid,methacrylic acid, itaconic acid, styrenesulfonic acid or its sodiumsalt, maleic acid, fumaric acid, citraconic acid, and the mixture of anycombination of them, and the like. The amount of the monomer having acarboxyl group may range from 10 to 65 weight percent, preferably from20 to 55 weight percent, of the polymeric shell wall. A polymeric shellwall containing less than 10 weight percent of the monomer having acarboxyl group cannot attain sufficient expansion of the resultantmicrocapsules at 200° C. or higher.

The monomers having an amide group are, for example, acryl amide,methacrylamide, N,N-dimethylacrylamide, and N,N-dimethylmethacrylamide.The preferable ratio of the monomer having an amide group ranges from0.1 to 20 weight percent, more preferably from 1 to 10 weight percent ofthe polymeric shell wall. A proper expanding performance ofmicrocapsules for each application can be attained by modifying theratio of the monomer having an amide group within the range of thepreferable ratio. Polymeric shell wall containing lower ratio of themonomer having an amide group results in microcapsules expandingnarrower temperature region, while polymeric shell wall containinghigher ratio of the monomer having an amide group results inmicrocapsules expanding broader temperature region. In other words,greater ratio of the monomer having an amide group in polymeric shellwall contributes to producing microcapsules having superior heatresistance.

The monomers having a cyclic structure in its side chain are, forexample, styrene, α-methyl styrene, chlorostyrene, isobornyl(meth)acrylate, and cyclohexyl methacrylate. Phenyl maleimide andcyclohexyl maleimide, which are monomers having a cyclic structure inits principal chain and having a cyclic structure in its side chain, arealso employed as the monomer having a cyclic structure in its sidechain. Preferable ratio of the monomer having a cyclic structure in itsside chain is 0.1 to 20 weight percent of polymeric shell wall, morepreferably 1 to 10 weight percent. A proper expanding performance ofmicrocapsules for each application can be attained by modifying theratio of the monomer having a cyclic structure within the preferablerange. Polymeric shell wall containing lower ratio of the monomer havinga cyclic structure in its side chain results in microcapsules expandingnarrower temperature region, while polymeric shell wall containinghigher ratio of the monomer having a cyclic structure results inmicrocapsules expanding broader temperature region. In other words,polymeric shell wall containing greater ratio of the monomer having acyclic structure in its side chain contributes to retaining theelasticity of expanded microcapsules in a wider temperature range.

Monomers having two or more of polymerizable double bonds in theirmolecules (cross-linking agents) can be optionally added to the shellpolymer, though the microcapsules of the present invention can beproduced without such cross-linking agents. The examples of thecross-linking agents are divinyl benzene, ethyleneglycoldi(meth)acrylate, diethyleneglycol di(meth)acrylate, triethyleneglycoldi(meth)acrylate, PEG (200) di(meth)acrylate, PEG (400)di(meth)acrylate, PEG (600) di(meth)acrylate, triacryl formal,trimethylolpropane trimethacrylate, aryl methacrylate, 1,3-butylglycoldimethacrylate, and triacryl isocyanate, though the applicablecross-linking agents are not restricted within the scope of thosemonomers. The preferable ratio of the cross-linking agents is 0 to 3weight percent of the polymeric shell wall. The addition of the monomerhaving two or more of polymerizable double bonds widens the range ofexpanding temperature of resultant microcapsules.

The polymeric shell wall of the microcapsules is produced by blending aproper amount of a polymerization initiator to the components describedabove. The applicable polymerization initiators are the compounds knownto those skilled in the art, such as peroxides and azo compounds. Theexamples of the polymerization initiators are azobisisobutylonitrile,benzoyl peroxide, lauryl peroxide, diisopropyl peroxidicarbonate,t-butyl peroxide, and 2,2′-azobis (2,4-dimethyl) valeronitrile, thoughthe applicable polymerization initiators are not restricted within thescope of those substances. The preferable polymerization initiators areoil-soluble initiators which are soluble in the polymerizable monomeremployed.

The preferable glass-transition point (Tg) of the polymer forming theshell wall of the thermo-expansive microcapsule is 120° C. or higher.The Tg of the polymer can be calculated from Tg of the homopolymer ofeach of monomers contained in the polymer, or can be determined withdifferential scanning calorimetry (DSC).

The blowing agents encapsulated in the microcapsules are those known toskilled in the art, which gasify below the softening point of thepolymeric shell wall. The examples of such blowing agents are propane,propylene, butene, normal butane, isobutane, isopentane, neopentane,normal pentane, normal hexane, isohexane, heptane, octane, nonane,decane, petroleum ether, halogenated compounds of methane,low-boiling-point liquid such as tetraalkyl silane, and thermallydegradable and gasifiable compounds such as AIBN. Those blowing agentsare selected according to the desirable range of the expandingtemperature of microcapsules. One of the blowing agents or two or moreof them are employed.

Although fluorine compounds such as HCF, HCFC, HFC, and HFE, which aregenerally called flon, fluorocarbon, and fluoroether, are also includedin the examples of the blowing agents mentioned above, they may not beused under the present situation where the destruction of ozone layerand the green-house effect of the earth are concerned.

For producing the thermo-expansive microcapsules of the presentinvention, conventional processes are usually employed. In thoseprocesses, inorganic particles such as silica, magnesium hydroxide,calcium phosphate and aluminum hydroxide, are applied as stabilizers foraqueous dispersion. In addition, condensation products of diethanolamineand aliphatic dicarboxylic acid, polyvinyl pyrolidone, methyl cellulose,polyethylene oxide, polyvinyl alcohol and various emulsifiers areapplied as the auxiliaries for those stabilizers.

In conventional processes, inorganic dispersants remained on polymericshell wall were assumed to be the cause of the agglomeration of driedmicrocapsules or poor dispersibility of microcapsules in medium, andstudies were carried out to remove the remained inorganic dispersants.

However, the inventors of the present invention have found thatinorganic dispersants remained on polymeric shell wall contribute toretaining the heat resistance of the thermo-expansive microcapsules ofthe present invention. In other words, it is estimated that inorganicdispersants remained on polymeric shell wall improve the heat resistanceof microcapsules by forming outer layer of polymeric shell wall or bygenerating synergy with the polar groups of polymeric shell wall.

The preferable ratio of the inorganic dispersant in thermo-expansivemicrocapsules is 1 to 25 weight percent, more preferably 5 to 20 weightpercent, for imparting heat resistance to thermo-expansive microcapsulesand dispersing thermo-expansive microcapsules in resin.

For producing foamed and molded products, the proper ratio of saidthermo-expansive microcapsules to rubber or resin ranges from 0.1 to 20weight percent, preferably from 0.5 to 12 weight percent and morepreferably from 1 to 6 weight percent.

The ratio of the thermo-expansive microcapsules should be adjustedaccording to the variants of molded products to be produced. Forexample, in the case of injection molding, a small ratio of saidthermo-expansive microcapsules is effective for improving surface finishand preventing wrinkles on product surface, and greater quantity of saidthermo-expansive microcapsules contributes to high foaming of moldedproducts.

The proper mean diameter of said thermo-expansive microcapsules is about1 to 500 μm, preferably about 3 to 100 μm, and more preferably 5 to 50μm. Thermo-expansive microcapsules of excessively small mean diametercannot foam the molded products enough and those of excessively largemean diameter produce large air bubbles which decrease the strength ofthe resultant foamed and molded products.

Thus an optimum particle diameter of microcapsules is selected accordingto the end uses of resultant products.

Said thermo-expansive microcapsules can be blended directly in rubber orresin, or can be blended in resin after mixed with thermoplastic resinand prepared into a master batch.

The applicable thermoplastic resins for mixing with the thermo-expansivemicrocapsules for preparing a master batch are polyorefins and theircopolymers. For example, ethylene vynil acetate, ethylbuthyl acrylate,ethylmethyl acrylate, polyethylene, polypropylene, styrene blockcopolymer and thermo-plastic elastomer.

The processes for producing the foamed and molded products includeconventional processes, such as calendering, extrusion, blow molding,injection molding, and internal cast molding.

The thermo-expansive microcapsules of the present invention havesuperior heat resistance and expand sufficiently at high temperature,such as 200° C. or higher temperature, and the expanded capsules areelastic. Thus the thermo-expansive microcapsules of the presentinvention can expand sufficiently in an admixture with rubber andresins, such as PE, PP, PS, and SBC, in the temperature region from 200°C. to higher, in which conventional thermo-expansive microcapsulescannot expand enough, to reduce the weight of molded products and tointroduce discrete air bubbles in molded products. In addition, thepresent invention can provide thermo-expansive microcapsules exhibitingsufficient expanding performance at 250° C. or above, and are applicableto foaming engineering plastics, super-engineering plastics, andthermo-setting resins, which cannot be foamed enough with other foamingagents, such as organic or inorganic foaming agents.

BEST MODE OF EMBODIMENT EXAMPLES

The present invention is described specifically with the followingexamples and comparative examples.

Example 1

An aqueous medium was prepared by adding 150 g of salt water, 3 g of anadipic acid-diethanolamine condensate, and 60 g of colloidal solution ofhydrated alumina in 500 g of deionized water and by homogenizing themixture with agitation.

An oily medium was prepared by mixing 120 g of acrylonitrile, 70 g ofmethacrylonitrile, 90 g of methacrylic acid, 10 g of methacrylamide, 10g of styrene, 1 g of azobisisobutylonitrile, 40 g of isohexane, and 40 gof isooctane, and by dissolving the component with agitation.

Then the aqueous medium and oily medium were mixed and agitated in ahomogenizer at 7000 rpm for 2 minutes to be prepared into suspension.Then the suspension was transferred in a reactor, purged with nitrogen,and reacted with agitation at 70° C. for 20 hours. The reacted productwas filtered and dried.

The resultant microcapsules had a mean diameter about 15 μm andcontained 12 weight percent of inorganic substances.

The thermo-expanding performance of the thermo-expansive microcapsuleswas analyzed with a TMA-7, a tester produced by Perkin-Elmer Co., Ltd.,according to the procedure disclosed in Japanese Patent Laid-Open No.Hei 11-002615.

As a result, the thermo-expansive microcapsules exhibited an initialexpanding temperature of 185° C. and a maximum expanding temperature of230° C.

Example 2

An aqueous medium was prepared by adding 150 g of salt water, 3 g ofadipic acid-diethanolamine condensate, and 40 g of colloidal solution ofhydrolyzed alumina in 500 g of deionized water and by homogenizing themixture with agitation.

An oily medium was prepared by mixing 120 g of acrylonitrile, 90 g ofmethacrylonitrile, 80 g of methacrylic acid, 5 g of methacrylamide, 5 gof styrene, 1 g of azobisisobutylonitrile, 40 g of isopentane, and 40 gof isooctane, and by dissolving the component with agitation.

Then the aqueous medium and oily medium were mixed and treated as in thesame manner in Example 1.

The resultant microcapsules had a mean diameter about 30 μm, contained 7weight percent of inorganic substances, and exhibited an initialexpanding temperature of 160° C. and a maximum expanding temperature of210° C.

Example 3

Thermo-expansive microcapsules were produced in the same manner as inExample 1, except that an oily medium was prepared by mixing 120 g ofacrylonitrile, 60 g of methacrylonitrile, 70 g of methacrylic acid, 40 gof acrylic acid, 5 g of methacrylamide, 5 g of styrene, 1 g ofazobisisobutylonitrile, 40 g of isohexane, and 40 g of isooctane, and bydissolving the component with agitation.

The resultant microcapsules had a mean diameter about 12 μm, contained15 weight percent of inorganic substances, and exhibited an initialexpanding temperature of 180° C. and a maximum expanding temperature of220° C.

Example 4

Thermo-expansive microcapsules were produced in the same manner as inExample 1, except that an oily medium was prepared by mixing 120 g ofacrylonitrile, 60 g of methacrylonitrile, 80 g of methacrylic acid, 20 gof acrylamide, 20 g of styrene, 1 g of azobisisobutylonitrile, 40 g ofisopentane, and 40 g of isooctane, and by dissolving the component withagitation.

The resultant microcapsules had a mean diameter about 20 μm, contained10 weight percent of inorganic substances, and exhibited an initialexpanding temperature of 160° C. and a maximum expanding temperature of210° C.

Example 5

Thermo-expansive microcapsules were produced in the same manner as inExample 1, except that an oily medium was prepared by mixing 100 g ofacrylonitrile, 30 g of methacrylonitrile, 140 g of methacrylic acid, 15g of methacrylamide, 15 g of styrene, 1 g of azobisisobutylonitrile, and80 g of isooctane, and by dissolving the component with agitation.

The resultant microcapsules had a mean diameter about 18 μm, contained10 weight percent of inorganic substances, and exhibited an initialexpanding temperature of 210° C. and a maximum expanding temperature of250° C.

Example 6

Thermo-expansive microcapsules were produced in the same manner as inExample 1, except that 0.5 g of ethyleneglycol dimethacrylate was addedto the oily medium.

The resultant microcapsules had a mean diameter about 20 μm, contained14 weight percent of inorganic substances, and exhibited an initialexpanding temperature of 190° C. and a maximum expanding temperature of235° C.

Example 7

Thermo-expansive microcapsules were produced in the same manner as inExample 1, except that the reaction was carried out at first at 70° C.for 7 hours and then at 90° C. for 13 hours.

The resultant microcapsules had a mean diameter about 20 μm, contained15 weight percent of inorganic substances, and exhibited an initialexpanding temperature of 190° C. and a maximum expanding temperature of270° C.

Example 8

A foamed rubber sheet was produced by preparing a rubber sheetcontaining thermo-expansive microcapsules with biaxial rolls and byheating the sheet.

Two weight percent of the thermo-expansive microcapsules produced in theprocess described in Example 2 was wet with 2 weight percent of aprocess oil and mixed with 96 weight percent ofstyrene-butadiene-styrene block copolymer (SBS). The mixture was kneadedwith biaxial rolls at 80 to 100° C. to be processed into a rubber sheet,and then heated with a hot pressing device at 170° C. for 10 minutes tobe processed into foamed rubber sheet.

The foaming of the mixture in the kneading with biaxial rolls and thefoaming in hot pressing were evaluated.

The result is shown in Table 1.

Comparative Example 1

A foamed rubber sheet was produced in the same manner as in Example 8except that the thermo-expansive microcapsules-1 (consisting ofpolymeric shell wall of acrylonitrile and methacrylonitrile, having amean diameter of about 30 μm, and exhibiting an initial expandingtemperature of 120° C. and a maximum expanding temperature of 170° C.)were employed instead of the thermo-expansive microcapsules of Example2.

The result is shown in Table 1. TABLE 1 State of rubber Surface ofrubber Specific gravity of foamed Test No. sheet (*1) sheet (*2) rubbersheet (g/cm³) Example 8 not expanded good 0.45 Comparative Example 1expanded poor 0.60(*1): Tested by inspecting the cross section of rubber sheets afterkneading through scanning electron microscope (SEM) to check theexistence of expanded microcapsules(*2): Tested by visual inspection of the roughness of rubber sheetsurface

The results compared in Table 1 described above show that thethermo-expansive microcapsules of the present invention, of whichpolymeric shell wall has a Tg (glass transition temperature) of 120° C.or higher temperature, did not expand with the heat generated in thekneading with rubber in the production process of foamed rubber sheet,and contributed to satisfactory surface finish of the rubber sheet. Thethermo-expansive microcapsules of the present invention sufficientlyexpanded in hot pressing to contribute to producing foamed rubber sheetof lower specific gravity and reduced weight.

Example 9

Foamed film sheet was produced with extruding.

A composition was prepared by mixing 96 weight percent of polyethylene(with a density of 0.91 g/cm³, and melt flow rate of 32 g/10 min at 190°C.), 3 weight percent of the thermo-expansive microcapsules produced inthe process in Example 1, and 1 weight percent of an oil. Thecomposition was processed into foamed film sheet with a T-dietemperature controlled at 200 to 220° C. The result is shown in Table 2.

Comparative Example 2

Foamed film sheet was produced in the same manner as in Example 9 exceptthat the thermo-expansive microcapsules-2 (consisting of polymeric shellwall of acrylonitrile, methacrylonitrile and methyl methacrylate, havinga mean diameter of about 18 μm, and exhibiting an initial expandingtemperature of 145° C. and a maximum expanding temperature of 155° C.)were applied instead of the thermo-expansive microcapsules of Example 1.The result is shown in Table 2. TABLE 2 T-die Sheet Color temperatureExpansion thickness (b value) Test No. (° C.) (%) (mm) (*3) Example 9200 1.28 0.45 0.02 210 1.44 0.50 0.04 220 1.87 0.52 0.05 Comparative 2001.00 0.33 0.57 Example 2 210 1.00 0.32 0.60 220 1.00 0.32 0.61(*3): Determined with a spectral colorimeter CLR-7100F produced bySHIMADZU Co., Ltd. according to the Hunter system of color. The b valuesindicate yellowing of test specimens, and greater value representsdeeper shade of yellow.

The results compared in Table 2 show that light-weight foamed film sheetwas produced with the thermo-expansive microcapsules of the presentinvention. The resultant film sheet was white without color change.

On the other hand, the thermo-expansive microcapsules in the film sheetsproduced in Comparative Example 2 may have shrunk with the heat in theextruding process. Thus no foaming was observed in the sheets thoughthey were colored.

Example 10

A composition described below was processed in injection-molding under ainjection pressure of about 1000 kg/cm² with an injection moldingmachine with a clamping force of about 80 tons and 32 mm screw diameter.

A composition was prepared by mixing 97 weight percent of polypropylene(with a density of 0.9 g/cm³, and melt-flow rate of 14 g/10 min at 230°C.) and 3 weight percent of thermo-expansive microcapsules produced inthe process of Example 6. The composition was processed ininjection-molding at 190 to 250° C. to be formed into a disc-shapedproducts having 98 mm diameter and 3 mm thickness. The result is shownin Table 3.

Example 11

A composition was processed in the same manner as in Example 10 exceptthat the thermo-expansive microcapsules produced in the process ofExample 7 were employed instead of the thermo-expansive microcapsulesproduced in the process of Example 6. The result is show in Table 3.

Comparative Example 3

A composition was processed in the same manner as in Example 10 exceptthat the thermo-expansive microcapsules-1 (consisting of polymeric shellwall of acrylonitrile and methacrylonitrile, having a mean diameter ofabout 30 μm, and exhibiting an initial expanding temperature of 120° C.and a maximum expanding temperature of 170° C.) were applied instead ofthe thermo-expansive microcapsules produced in the process of Example 6.The result is shown in Table 3.

Comparative Example 4

A composition was processed in the same manner as in Example 10 exceptthat the thermo-expansive microcapsules-3 (consisting of polymeric shellwall of acrylonitrile, methacrylonitrile and methacrylic acid, having amean diameter of about 30 μm, and exhibiting an initial expandingtemperature of 160° C. and a maximum expanding temperature of 200° C.)were applied instead of the thermo-expansive microcapsules produced inthe process of Example 6. The result is show in Table 3. TABLE 3Injection Density Reduced Test No. temperature (° C.) (g/cm³) weight (%)Example 10 190 0.71 21 210 0.66 27 230 0.67 26 250 0.69 23 Example 11190 0.71 21 210 0.66 27 230 0.63 30 250 0.61 32 Comparative 190 0.72 20Example 3 210 0.81 10 230 0.84 7 250 0.87 3 Comparative 190 0.67 26Example 4 210 0.72 20 230 0.77 14 250 0.83 8

The results compared in Table 3 show that the foamed and molded productswith the thermo-expansive microcapsules of the present inventionresulted in satisfactory expanding in wide temperature range.

In other words, the production process for producing foamed and moldedproducts of the present invention can constantly produce foamed andmolded products with high foaming.

In addition, the foamed and molded products produced with thethermo-expansive microcapsules described in Comparative Examplesresulted in smaller weight reduction in injection molding at highertemperature levels, of which cause was estimated to be the shrinkage ofexpanded microcapsules. Simultaneously color change was observed onthose products. On the contrary, the foamed and molded products with thethermo-expansive microcapsules of the present invention resulted insufficient foaming and slight color change.

Example 12

A composition was prepared by mixing 99 weight percent of polypropyleneand 1 weight percent of thermo-expansive microcapsules produced in theprocess of Example 6, and processed in the same manner as in Example 10except that the injection was carried out at 210° C.

Example 13

A composition was prepared by mixing 95 weight percent of polypropyleneand 5 weight percent of thermo-expansive microcapsules produced in theprocess of Example 6, and processed in the same manner as in Example 10.

The results of Examples 10, 12, and 13 are compared in Table 4. TABLE 4Injection Density Reduced Test No. temperature (° C.) (g/cm³) weight (%)Example 10 210 0.66 27 (PP & 3 wt. % of capsules) Example 12 210 0.76 16(PP & 1 wt. % of capsules) Example 13 210 0.58 36 (PP & 5 wt. % ofcapsules)

The comparative result in Table 4 shows that the weight reduction ofresultant products can be controlled by changing the ratio ofthermo-expansive microcapsules.

APPLICATION IN INDUSTRIAL FIELDS

The thermo-expansive microcapsules, production process for foamed andmolded products, and foamed and molded products therefrom described inclaims 1 to 7 provide thermo-expansive microcapsules which exhibitsuperior heat resistance and sufficient expanding performance at 200° C.or higher, and expand into elastic balloons. In addition, a mixture ofthe thermo-expansive microcapsules of the present invention and rubberor resin such as PE, PP, PS, and SBC, exhibits high foaming performancethat were not attained by conventional thermo-expansive microcapsules,i.e., foaming sufficiently in heating at 200° C. or higher to introduceair bubbles in products and to reduce their weight. The presentinvention also provides thermo-expansive microcapsules having superiorexpanding performance in high temperature region, 250° C. or higher, andhaving a great possibility of the application in industrial fields owingto their applicability to foaming engineering plastics, superengineering plastics and thermo-setting resins, which could not beattained by other foaming agents, such as organic or inorganic foamingagents.

1. A thermo-expansive microcapsule comprising: a polymeric shellproduced by polymerizing monomer components containing 15 to 75 weight %of a nitrile monomer, 10 to 65 weight % of a monomer having a carboxylgroup, 0.1 to 20 weight % of a monomer having an amide group and 0.1 to20 weight % of a monomer having a cyclic structure in its side chain;and a blowing agent encapsulated in the polymeric shell.
 2. Thethermo-expansive microcapsule of claim 1, wherein the polymeric shell isproduced by polymerizing the monomer components further containing 3weight % or less of a monomer having at least two polymerizable doublebonds (a cross-linking agent).
 3. The thermo-expansive microcapsule ofclaim 1, wherein the polymeric shell has a glass transition point (Tg)of 120° C. or higher.
 4. The thermo-expansive microcapsule of claim 1,wherein the polymeric shell contains 1 to 25 weight % of inorganiccompounds.
 5. The thermo-expansive microcapsule of claim 1, which has amaximum expanding temperature of 200° C. or higher.
 6. A productionprocess of a foamed and molded product which comprises adding thethermo-expansive microcapsule of claim 1 in rubber or resin to form amixture and heating the mixture to expand the thermo-expansivemicrocapsule to introduce discrete air bubbles in the product.
 7. Afoamed and molded product containing the thermo-expansive microcapsuleof claim 1.